IRESSA^® (gefitinib tablets) contain 250 mg of gefitinib and are available as brown film-coated tablets for daily oral administration.

Gefitinib is an anilinoquinazoline with the chemical name 4-Quinazolinamine, N-(3-chloro-4- fluorophenyl) -7-methoxy-6- [3-4-morpholin) propoxy] and the following structural formula:

It has the molecular formula C₂₂H₂₄ClFN₄O₃, a relative molecular mass of 446.9 and is a white-colored powder. Gefitinib is a free base. The molecule has pK_aS of 5.4 and 7.2 and therefore ionizes progressively in solution as the pH falls. Gefitinib can be defined as sparingly soluble at pH 1, but is practically insoluble above pH 7, with the solubility dropping sharply between pH 4 and pH 6. In non-aqueous solvents, gefitinib is freely soluble in glacial acetic acid and dimethylsulphoxide, soluble in pyridine, sparingly soluble in tetrahydrofuran, and slightly soluble in methanol, ethanol (99.5%), ethyl acetate, propan-2-ol and acetonitrile.

The inactive ingredients of IRESSA tablets are: Tablet core: Lactose monohydrate, microcrystalline cellulose, croscarmellose sodium, povidone, sodium lauryl sulfate and magnesium stearate. Coating: hypromellose, polyethylene glycol 300, titanium dioxide, red ferric oxide and yellow ferric oxide.

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